1. Field of the Invention
The present invention relates to a negative planographic printing plate precursor. The invention relates in particular to a planographic printing plate precursor that can be used in plate-making by scan-exposure based on digital signals, can provide contaminant-free prints, having high sensitivity and high printing resistance, and can be disposed in a printer directly without particular development after image formation.
2. Description of the Related Art
Numerous studies have been made on printing plates for the computer-to-plate system, where development has been significant in recent years. In these studies, in order to further simplify the printing process and solve the problem of waste solution disposal, a development-free planographic printing plate precursor that can be used in printing without development after light exposure by directly disposing it in a printer has been studied, and various methods have been proposed.
To eliminate any treatment steps of the printing process, there is a method called development in a machine, wherein an exposed planographic printing plate precursor is disposed on a cylinder in a printer, and the non-image part of the planographic printing plate precursor is removed by rotating the cylinder and supplying moistening water and ink thereto. That is, the planographic printing plate precursor is exposed to light and directly disposed in a printer, whereby processing can be concluded in the process of ordinary printing.
It is necessary that the planographic printing plate precursor suitable for development in a machine has a photosensitive layer soluble in moistening water and an ink solvent, and can be handled in a bright room so as to be suitable for development in a printer placed in a bright room.
For example, Japanese Patent No. 2938397 discloses a planographic printing plate precursor comprising a hydrophilic substrate having disposed thereon a heat-sensitive layer having fine thermoplastic hydrophobic polymer particles dispersed in a hydrophilic binder polymer. In this patent, it is disclosed that the planographic printing plate precursor can be developed in a machine by thermally fusing the fine thermoplastic hydrophobic polymer particles upon exposure to an infrared laser to form an image on the plate, then disposing the plate on a cylinder in a printer, and developing the plate in the printer with moistening water and/or ink.
In such a method of forming an image by mere heat fusion, the non-image region on the recording layer has good development performance in the machine, but the strength of the image region is weak and printing resistance is insufficient. Further, when the heat-sensitive layer is disposed directly on an aluminum substrate generally used as the substrate for a planographic printing plate precursor, heat generated by light exposure is removed by the highly heat-conductive aluminum substrate so that, in the vicinity of an interface between the substrate and the heat-sensitive layer, the heat energy cannot be sufficiently used in image formation, i.e., in heat fusion of the fine particles, whereby the image region cannot be sufficiently hardened and printing resistance is insufficient.